1. Field
The present disclosure relates to magnetoresistive elements and memory devices including the same.
2. Description of the Related Art
Magnetic random access memories (MRAMs) are memory devices that store data by using resistance variation of a magnetic tunneling junction (MTJ) element. Resistance of the MTJ element varies according to the magnetization direction of a free layer. In other words, when the magnetization direction of a free layer is identical with that of a pinned layer, the MTJ element has low resistance. When the magnetization direction of the free layer is opposite to that of the pinned layer, the MTJ element has high resistance. If the MTJ element has low resistance, data may correspond to ‘0’. On the other hand, if the MTJ element has high resistance, data may correspond to ‘1’. MRAMs attract attention as one of the next-generation non-volatile memory devices due to their merits, for example, non-volatility, high-speed operation, and/or high endurance.
Thermal stability of data stored in an MTJ element is related to an energy barrier (Eb) of a free layer. It has been known that, when a free layer is an in-plane magnetic anisotropic material layer and Eb/kBT (where kB is the Boltzmann constant and T is the absolute temperature) is about 60, the thermal stability of the MTJ element is ensured for about 10 years. In general, the feature size of the MTJ element (that is, the feature size of the free layer) should be at least about 40 nm for ensuring a relatively high Eb/kBT of about 60, although it may slightly vary according to the thickness of the free layer. This means that it is difficult to reduce the feature size of the MTJ element to less than 40 nm. Thus, it is difficult to increase the recording density of an MRAM to a set level.